Successful Management of Two Consecutive Pregnancies With Maternal–Fetal Phenylketonuria: Lessons From Clinical Practice

Phenylketonuria (PKU) is an autosomal recessive disorder caused by a deficiency of phenylalanine hydroxylase (PAH), leading to the accumulation of phenylalanine (Phe) and an increased risk of developmental disorders. Treatment involves a Phe-restricted diet, amino acid supplements, and for a subset of patients, a tetrahydrobiopterin (BH4) chaperone. Managing PKU during pregnancy is challenging due to changing protein and energy needs, stricter Phe control, nausea, and unpalatable supplements. In rare cases of simultaneous maternal and fetal PKU, Phe tolerance may increase less throughout gestation, raising the demands on the patient and caregivers. There are few reports and no guidelines on the management of PKU during pregnancies in which both mother and fetus have PKU, hereafter referred to as maternal-fetal PKU (mfPKU). This report outlines our approach for successfully managing two consecutive mfPKU pregnancies. We emphasize a patient-centered approach, focusing on patient education and close collaboration with a multidisciplinary metabolic team. This involves regular monitoring of body weight, blood Phe levels, and calorie intake through an online food diary to tailor individual recommendations for natural protein restriction and amino acid supplements.